1. Field of the Invention
The present invention relates to a focus-detecting device, and more particularly, to a focus-detecting device used to detect a focus state of a photographic lens in a camera or similar mechanism.
2. Description of Related Art
Numerous focus detection devices using a phase difference method have been developed for cameras and similar mechanisms. Light rays passing through different regions on an exit pupil of a photographic lens are composed into images on a pair of light-receiving components in a line sensor after passing through a field lens and a pair of re-imaging lenses. The focus state of the photographic lens is detected from the positional relationship of the pair of images.
FIG. 11 shows one type of a conventional focus detection device using this method. In this focus detection device, light rays L1-L4 passing through different regions of the exit pupil 1 of the photographic lens pass through a field mask 2, which determines the range of the distance measuring areas and which is positioned near the predetermined focal plane of the photographic lens. Light rays L1-L4 are composed into images on the line sensor 6 by a re-imaging lens 5 after passing through an aperture mask 4.
The focus detection device comprises a so-called cross-type device. The re-imaging lens 5 includes two pairs of lens components 5a, 5b, 5c and 5d. The line sensor 6 includes two pairs of light-receiving components 6a, 6b, 6c and 6d. Corresponding focus state detection areas are formed of intersecting areas that extend in different directions so as to intersect. By arranging the pairs of lenses 5a, 5b, 5c and 5d and light-receiving components 6a, 6b, 6c and 6d perpendicularly, distance measurement is possible for objects in all directions. Even when an object extends parallel to one of the distance measurement areas in the photographic field, distance measurement is possible with the other distance measurement areas.
Conventionally, several such focus detection devices include a cross-type arrangement, which has a plurality of focus state detection optical systems and in which distance measurement is possible in a plurality of areas in the photographic field.
FIG. 12 shows one example of such a device, in which a focus detection device includes three cross-type focus state detection optical systems as shown in FIG. 11, arranged in a line, so that distance measurement is accomplished at three locations in the photographic field. With this focus detection device, cross-type distance measurement is possible not only in the intersecting areas A (FIG. 13) in the center of the photographic field P, but also in the intersecting areas B and C to the left and right of the center. Furthermore, with this focus detection device, the field masks 12, the field lenses 13, the aperture masks 14, the re-imaging lenses 15 and the line sensors 16 each are constructed integrally as single units to provide compactness.
However, in the focus detection device of FIG. 12, images on the predetermined focal plane are formed by the re-imaging lens 15 on the line sensor 6 as shown in FIG. 14. The focus state is detected by converting each of the images 21a, 21b, 21c and 21d into an electrical signal by means of the light-receiving components 6a, 6b, 6c and 6d on the line sensor 16, i.e. the intersecting areas detection unit 23, and by processing the electrical signals.
Furthermore, the positioning of the images 21a, 21b, 21c and 21d and the light-receiving components 6a, 6b, 6c and 6d can be skewed, as shown in FIG. 15, because of skewing of the mutual positioning of the lenses 5a, 5b, 5c and 5d and the light-receiving components 6a, 6b, 6c and 6d. Light-receiving components 6a-6d are in pairs 6a-6b and 6c-6d, and perform focus state detection in the same regions of the photographic field P. Components 6a-6d receive light rays from different areas in the photographic field P. Consequently, accurate focus state detection cannot be accomplished. Accordingly, in such a case, it often is necessary to adjust positioning by moving the line sensor 6 as a whole in the re-imaging plane to achieve the state shown in FIG. 14.
However, it is extremely difficult to adjust the position of the line sensor 16 in a focus detection device such as shown in FIG. 12, for example, in which the line sensor 16, on which are positioned three intersecting areas detection units 23A, 23B and 23C, is in a single line sensor package. For example, as shown in FIG. 16, consider the case when the positional relationship between the four images 21a, 21b, 21c and 21d and the light-receiving components 6a, 6b, 6c and 6d agree in the intersecting areas detection units 23A and 23C as a result of adjustment. If the positional relationship between the four images 21a, 21b, 21c and 21d and the light-receiving components 6a, 6b, 6c and 6d is skewed in the intersecting areas detection unit 23B, it is impossible to adjust the mutual positions of the four images 21a, 21b, 21c and 21d and the light-receiving components 6a, 6b, 6 c and 6d in the intersecting areas detection unit 23B without destroying the positional relationship between the four images 21a, 21b, 21c and 21d and the light-receiving components 6a, 6b, 6c and 6d in the intersecting areas detection units 23A and 23C.
For this reason, because the three intersecting areas detection units 23A, 23B and 23C are in a single line sensor 16 package, when the line sensor 16 package is rotated to adjust the position in intersecting areas detection unit 23B, the positional relationship is destroyed in intersecting areas detection units 23A and 23C, in which the positions agreed prior to the adjustment.
The same problem exists in focus detection devices in which two intersecting areas detection units are in a single line sensor package, and is a problem common to all devices wherein a plurality of intersecting areas detection units are collected into a single line sensor package.